- Synonyms: Leukocytes, Leucocytes, White blood cells, WBCs
- White blood cells (WBCs) are essential components of the immune system, responsible for defending the body against infections, foreign invaders, and abnormal cells.
- They circulate in the blood and lymphatic system and can move into tissues where they are needed.
- Unlike red blood cells, white blood cells have a nucleus and come in various types, each with specialized functions.
- Though they make up only about 1% of the total blood volume, their role is crucial in maintaining the body’s defense mechanisms.
- White blood cells are broadly categorized into two main groups: granulocytes and agranulocytes.
- Granulocytes, characterized by the presence of granules in their cytoplasm, include neutrophils, eosinophils, and basophils.
- Neutrophils, comprising approximately 50-70% of all WBCs, are the most abundant and often the first to respond to infection, engulfing and destroying bacteria and debris through phagocytosis.
- Eosinophils, making up 1-4% of WBCs, combat parasitic infections and participate in allergic reactions.
- Basophils, though less than 1% of WBCs, play a crucial role by releasing histamine and other chemicals important in the inflammatory response.
- The agranulocytes consist of lymphocytes and monocytes.
- Lymphocytes, accounting for 20-40% of WBCs, include three main types: B cells, T cells, and natural killer (NK) cells.
- B cells produce antibodies to neutralize pathogens, while T cells help regulate immune responses and kill infected or cancerous cells. NK cells are involved in the early defense against viruses and tumors.
- Monocytes, comprising 2-8% of WBCs, are the largest type and develop into macrophages and dendritic cells once they migrate into tissues, where they detect harmful invaders and orchestrate longer-term immune responses.
- The production of WBCs occurs in the bone marrow through a process called hematopoiesis.
- WBC numbers in the bloodstream can fluctuate in response to infections, inflammation, stress, or diseases such as leukemia. A normal white blood cell count typically ranges from about 4,000 to 11,000 cells per microliter of blood, and deviations from this range can indicate underlying health conditions that may require medical attention.
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